Probe microscope setup method

ABSTRACT

A scanning probe microscope and method of operation for monitoring and assessing proper tracking between the tip and sample, as well as automating at least some aspects of AFM setup previously done manually. Preferably, local slopes corresponding to the acquired data are compared to determine a tracking metric that is self-normalizing.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 11/203,506 filed Aug. 12, 2005, now U.S. Pat. No. 7,513,142, issuedApr. 7, 2009, the entirety of which is expressly incorporated byreference herein.

FIELD OF THE INVENTION

The present invention is directed to a method and arrangement forautomating the setup of a probe microscope such as an atomic forcemicroscope (AFM), and more particularly to a method and arrangement ofautomatically adjusting AFM parameters and in doing so being alsocapable of self-adjusting AFM operation.

BACKGROUND OF THE INVENTION

Probe-based instruments obtain information via interaction between itssensing element and a sample being analyzed. One such instrument that istypically used for nano-scale and even atomic-scale analysis is a typeof scanning probe microscope (SPM) referred to as an atomic forcemicroscope (AFM). It is very versatile because it can analyze conductiveand non-conductive samples since the sample may not be electricallycharged during operation.

The sensing element of an AFM is a probe that interacts with the sampleduring operation to obtain information about the sample, such as size,surface contour or topography, shape, roughness, atomic makeup,molecular makeup, and/or other characteristics. The cantilever oftenincludes a probe tip, e.g., stylus, and is scanned over the sample bymoving it and/or the sample relative to one another in a mannerpreferably in a raster scan pattern. The analysis produces data fromtip-sample interaction at numerous locations of the scan, which often isused, for example, to generate a topographic image depicting the outersurface of the sample that was scanned. More generally an SPM measuresany number of properties of a sample, including for example surfacetopography, magnetic forces, electric forces, temperature, thermalconductivity, electrical properties, friction, elasticity, adhesion,just to name a few. These and other data representative of sampleproperties are typically measured by using a probe and detection systemthat can convert a probe sample interaction into data that is indicativeof the property of interest. For example, in the case of magneticmeasurements, an AFM tip is coated with a magnetic material and theresulting force between a sample region and the AFM tip is detected.

The cantilever and tip (where so equipped) form a probe that is receivedin a mount, e.g., probe mount, of the AFM. An AFM probe has at least onecantilever that extends outwardly from a support typically referred toas a base, substrate or chip and that can be part of the mount. Thecantilever typically is elongate, narrow and relatively small to achievenano-scale and atomic-scale imaging. For most such applications, thecantilever usually is no longer than about 500 microns and no wider thanabout 50 microns, and typically much smaller. The tip is also quitesmall and usually quite sharp, typically having a radius or diameterbetween three and fifty nanometers.

During operation, the cantilever is scanned over the sample, typicallyin a raster pattern, to analyze the sample. As the cantilever movesalong the sample surface, its tip can move up, such as when a bump onthe sample is encountered, can move down, such as where there is adepression or sidewall in the sample, and, in certain instances, canmove side-to-side, such as when friction is encountered or when CDimaging of semiconductor sidewalls is performed.

Relative movement between the sample and cantilever is controlled tohelp position the tip so it either contacts the sample or is closeenough to the sample that interaction between the cantilever tip andsample occurs. This interaction can be caused by friction, such astip-sample friction, molecular force, including strong and weak, e.g.,van der Waals, molecular forces, as well as magnetic force, for example.This interaction is desired because it is measured during operation toanalyze the sample, including when imaging the sample.

Controlling relative movement can be done in many ways but typically isachieved using one or more selectively controllable actuators. Theseactuators, typically of piezoelectric construction, are used to eithermove the cantilever relative to the sample, the sample relative tocantilever, and, in some instances, both of them at the same time. Forexample, in one well know arrangement, at least one actuator is used tomove the cantilever, and hence its tip, toward or away from the samplealong the Z-axis. One or more actuators are typically used to providerelative movement between the cantilever and sample along either or boththe X-axis and the Y-axis. One well known positioning device used inAFMs employs one or more actuator that provides motion in up to threeorthogonal dimensions, and is referred to as a scanner. Suitableexamples of such high-resolution, three axis scanners are disclosed inHansma et al. U.S. Pat. No. RE 34,489; Elings et al. U.S. Pat. No.5,226,801; and Elings et al. U.S. Pat. No. 5,412,980. The scanner may bea single unit that provides motion in three directions or may be madefrom discrete units. As mentioned above, the relative scan motion can becreated by scanning the probe, scanning the sample, or any combinationthereof. For example, some AFMs are constructed to scan the sample inthe XY direction and actuate the probe in the Z-direction.

As the sample is scanned during AFM operation, the cantilever deflectsin response to interaction with the sample. A detector is used tomeasure this interaction, typically by measuring cantilever deflection.This is because changes in interaction force, such as due to a change insample surface height or sample surface roughness, cause cantileverdeflection to change in a corresponding, even proportional, manner.Therefore, measuring the changes in cantilever deflection that occurduring scanning provide information from which various samplecharacteristics, including the contour of its out surface, can beobtained.

One commonly used detector uses the cantilever as an optical lever thatreflects a beam impinging against it during scanning. Any change incantilever deflection causes a corresponding change in the incidentangle of the reflected beam, which is measured by measuring reflectedbeam movement using an optical sensor on which the reflected beamshines. One suitable and preferred optical sensor uses one or morephoto-detector sensors or the like arranged in an array, such as in aside-by-side or even quadrature array, to sense any changes in reflectedbeam position. During scanning, output from the array is collected andprocessed so as to enable an image of the sample surface scanned by thecantilever to be produced in a manner where it can be displayed,printed, further analyzed, etc. An example of one such detector suitablefor AFM use is disclosed in Hansma et al. U.S. Pat. No. RE 34,489, whichuses a laser to produce the beam for the optical lever arrangement.

Since AFMs are often capable of operating in more than one mode, thenature of interaction between the cantilever and sample is usually, ifnot always, mode dependent. For example, a cantilever of an AFMoperating in contact mode will encounter a different type and magnitudeof interaction than when operating in a non-contact mode, e.g.,oscillating mode. Where contact is direct, interaction obviously tendsto be direct as forces are directly transmitted between the cantileverand sample. Where interaction is less direct, such as when it isindirect, e.g., non-contact mode, the nature of cantilever-sampleinteraction can prove relatively complex. For example, it is not unusualfor interaction to be due to one or more of weak molecular forceattraction, such due to Van der waals forces, stronger atomic-basedforces, repulsive forces, and adhesive forces due to contact with ahydrophilic layer on top of the sample, which also can be dependent onthe makeup of the sample as well as how close the cantilever tip is tothe sample.

In contact mode operation, the probe is typically scanned across thesurface of the sample while keeping the force of the tip of the probeagainst the surface of the sample generally constant. This is usuallyaccomplished by moving either the sample or the probe verticallyrelative to the surface of the sample being analyzed in response tosensed deflection of the cantilever as the probe is scanned generallycontinuously across the surface of the sample. Vertical motion feedbackinformation can be stored, along with other tip-sample interactionfeedback information, and used in constructing an image or the likerepresentative of the surface of the sample that corresponds to thesample characteristic being measured, e.g., surface topography.

Depending on the AFM, some AFMs can operate in different types ofoscillation modes including where the oscillation frequency is tied to aresonant frequency of the cantilever. Feedback normally is used to keepa parameter of cantilever oscillation (e.g., amplitude, phase,frequency) constant. The information providing the feedback typically isat least partly based on cantilever-sample interaction, e.g., tip-sampleinteraction, taking place during operation. As is preferably also thecase with contact mode operation, information obtained usingcantilever-sample feedback is collectable, storable, and usable as datato analyze the sample, including by characterizing it as well as imagingit.

One particularly advantageous and versatile oscillating mode isTappingMode™ AFM (TappingMode™ is a trademark owned by Veeco InstrumentsInc. of Santa Barbara, Calif.), which is implemented by oscillating thecantilever at a frequency at or near its resonant frequency. Cantileveroscillation amplitude, phase or frequency preferably is keptsubstantially constant via feedback, information for which is obtainedfrom the cantilever-sample interaction, e.g., tip-sample interaction,that takes place during operation. In intermittent contact orTappingMode AFM the tip only periodically contacts the sample surfacegenerally according to the drive signal, thus making it a lower forcemode operation than a mode such as contact mode where the tip and sampleare substantially continuously engaged.

No matter which operational mode is chosen, setup and operation of ameasurement instrument as complex and versatile as an AFM can be timeconsuming and tricky, especially for a novice AFM operator. For example,setup and operating parameter values typically depend on factors such asthe type of sample material including whether it is hard or soft,conductive or non-conductive, organic, synthetic or biological innature, among other things.

While past attempts have been made with AFMs to automatically adjustgain to minimize the difference between trace and retrace data, thismethod also has not proven particularly effective. For example, it maynot be able to handle sample topography and operating parameters, suchas, setpoint, actuator hysteresis and tip shape, which can unpredictablyand adversely impact trace-retrace differential data such that anyattempt to control it through gain adjustment is largely ineffective.

This is not surprising in view of the numerous scan parameters that mustbe taken into account in AFM setup and operation along with those thatcan require adjustment during operation. For example, a user may need toadjust such scan control parameters as setpoint, scan speed,proportional gain, integral gain, drive frequency, drive amplitude andother parameters. Without great care, considerable experience, andsometimes a little luck, tip, cantilever or sample damage can occur,poor or unusable results can be obtained, and, in instances whereeverything appears to go well, operation inefficiencies can be so greatthat scanning time is nowhere near optimal thereby wasting aconsiderable amount of time, which is particularly problematic for highthroughput applications such as those of the semiconductor industry.

For example, at present, if the value any one of several controlparameters manually selected is not at or within a reasonable range ofits optimum, poor performance and unacceptable data will very likelyresult. In addition, relatively complex interdependencies existingbetween certain AFM parameters often make setup a trial and errorprocedure, even for the most experienced AFM operators.

In performing AFM setup, the values for several control parameters mustbe set along with feedback loop gains for different operational modesand other instances where setting up such gains is required. Setup musttake into account and configure for parameters such as scan size, pixelsper line, number of scan lines, scan rate, tip scanning speed,digital-to-analog (D/A) resolution, Z-center position, i.e., Z-centervoltage or the center of the Z piezo operation range, tip wear control,and sample damage minimization. When an AFM is set-up to operate inoscillatory mode, such as TappingMode™, setup must include choosing anamplitude and setpoint associated with the oscillation.

When an AFM is going to operate in an oscillatory mode, such asTappingMode™, initial values for integral gain, i.e., I-gain, andproportional gain, i.e., P-gain, may also be manually set. Selectinggain values can be tricky because it typically depends on factors suchas the nature of the oscillatory mode being employed, sample topography,the type of sample and medium in which it is located, as well as otherfactors. For example, where gain is set too low, system response tendsto be relatively slow, which can result in the tip not following thesample surface. Where set too high, the feedback loop can startoscillating or backfeeding upon itself, which can undesirably addconsiderable noise to the sample image being generated.

In addition, the initial gain setup may be fine initially, only to beunsuitable later, such as when topography changes. For instance, wherethe sample is relatively rough, gain typically should be set higher inorder to image such high featured topography with any resulting increasein feedback oscillation noise being tolerable. Where the sample isrelatively smooth or flat, gain should be set lower to minimize noise.By keeping noise low by keeping gain low, better resolution of flatareas is achieved thereby enabling the AFM to better image its finerdetails. However, as understood in the field, excessive noise canadversely affect imaging along flatter areas of the sample where aninitially high gain setting ends up being too high when the sampleflattens out. Conversely, an initial low gain setting frequently impedesimaging of higher features of the sample producing an image with suchhigher features being either distorted or missing.

These setup considerations become even more problematic when operatingin an oscillating mode, such as TappingMode™. For example, since thehighest useable gains when operating in TappingMode™ typically depend oncantilever dynamics, setting gains becomes further complicated becausecantilever dynamics, in turn, is a function of the free air tappingsetpoint. Indeed, factors such as cantilever dynamics and Z-actuatorresponse speed can create such difficulty in setting the initialsetpoint and gains, the operator often resorts to trial and error untilthe sample image starts to look good.

Unfortunately, because one can affect the other, trial and error can goon for a long time. For example, as setpoint is lowered, gain can be sethigher and vice versa. However, while lower gains permit a lowersetpoint to be used, which typically increases cantilever response, italso increases error generation rate, which can undesirably blur orotherwise distort the image being produced during scanning.

In the end, what often results is the operator setting some initialparameter values, gains and setpoint, and then manually adjusting thevalue of each, one-by-one until feedback oscillation occurs and thenbacks off. While this process may work reasonably well for experiencedAFM operators, it is inefficient, time consuming, and quite often, lessthan optimal. In addition, it does nothing to address the dynamic natureof AFM imaging, which often requires an operator to either changecertain settings on the fly during operation or to observe the image,etc., and go back and re-scan those parts of the sample that are poorlyimaged with adjusted parameter values. Once again, extremely slow,inefficient and non-optimal.

Expert user intervention is typically also required during pre-scan orimage acquisition processes to maintain probe-sample interactionaccording to the mode of operation. The above-described scanning probemicroscopes (SPM) employ a uniaxial feedback control system to maintainprobe-sample interaction while scanning. That is, such a system iscapable of actuating to alter probe-sample distance along the Z-axis,and also of sensing probe response to sample surface position along theZ-axis. Moreover, SPM engage establishes initial probe-sampleinteraction, whether continuous or intermittent. Successful maintenanceof a continuous (contact mode) or intermittent (TappingMode™) targetinteraction while scanning in a direction other than Z demonstrates goodtracking of the sample surface by the probe.

Such tracking fails when the probe ceases to interact with the sample.This is more apt to happen under any of the following conditionsincluding, but not limited to, (1) in the scan direction, the samplesurface slopes away from the probe; (2) the SPM is scanning rapidly; (3)the feedback loop gain is set low; and (4) at the chose setpoint,probe-sample interaction is weak. In one known tracking measurementtechnique, a trace-minus-retrace (TMR) operation may be performed.Wherein the same N (e.g., 512) consecutive data acquisitions on thesample surface measured scanning in one direction, are individuallysubtracted from samples taken from obstensibly the same sites in reverseorder during retrace of the same sample surface line. Problems have beendemonstrated with this technique and thus an improvement has beendesired in the AFM field.

Hence the need has arisen for a method and arrangement that is able toautomate AFM setup, and do so to achieve optimal tracking between thetip and sample. What is further needed is the same or a like methodcapable of being used during actual AFM scanning.

SUMMARY OF THE INVENTION

The preferred embodiments are directed to a probe type microscopemeasurement instrument and method of operation for monitoring andassessing proper tracking between the tip and sample, as well asautomating at least some aspects of AFM setup previously done manuallyand performing a pre-scan that facilitates determining a value of one ormore optimum measurement instrument operating parameters under therequirement that the tip wear and sample damage are minimized during theoptimizing process. Tracking analysis can be carried out using pre-scanor normal operation scan data to determine whether tracking isacceptable or not. Tracking qualification can then be used to select orotherwise adjust a value of at least one measurement instrumentoperating parameter so as to improve tracking and otherwise optimizesetup.

The measurement instrument includes a probe that includes a cantileverthat can have a tip which interacts with a sample during operation in amanner from which data is obtained that can be used to analyze thesample. One such preferred measurement instrument well suited for thepresent invention is a scanning probe microscope, such as a scanningtunneling microscope or scanning force microscope.

One particularly preferred measurement instrument is a scanning forcemicroscope also known as an atomic force microscope (AFM). Such an AFMpreferably includes a probe with at least one cantilever that can beequipped with a tip at or adjacent its free end, a probe mount orholder, an arrangement, such as a scanner, that enables relativepositioning of the probe and sample, a detector that is linked to orwhich otherwise cooperates with the probe to obtain cantilever-sampleinteraction related data during operation, and a controller that canalso process the cantilever-sample interaction related data, if desired.For example, where the measurement is an AFM, the detector can be of anoptical lever configuration, such as is commonly used in the art.However, where the measurement instrument is, for example, an STM, thedetector preferably is configured to measure or otherwise senseelectrical activity associated with interaction with the sample duringoperation.

In the practice of a method in accordance with the present invention, aprocessor is linked to the measurement instrument in a manner thatenables it to facilitate carrying out one or more of measurementinstrument setup, monitoring, control, and operation. In one preferredembodiment, the processor is disposed onboard the controller, e.g., thecontroller processor, and can be a microcontroller, microprocessor,field-programmable gate array, etc. or some combination of one or morethereof. In another preferred embodiment, the processor can be made upof like components or possess a similar architecture but be locatedoffboard the controller and linked to the measurement instrument.Indeed, the present invention contemplates different processors beingresponsible for implementing or otherwise carrying out different steps,elements, or aspects of the method of the present invention.

The method of the invention is directed to automated measurementinstrument setup, automated measurement instrument tuning oroptimization, employing a pre-scan to facilitate tuning or optimization,as well as performing tracking quality determination. It will alsoautomatically display error messages and warnings if it detectsfailures. It should be noted that each of these can be implementedalone, in combination with one or more than one, or altogether,including during actual measurement instrument operation if desired. Theability to separate, combine, aggregate these things advantageouslyresults in a flexible, highly configurable and measurement instrumentadaptable method capable of numerous different implementations. Thisshould be kept in mind with regard to the following summary and detaileddescription of the invention as the disclosure that follows many timesgroups or links things together for the sake of convenience or claritywhen that need not always be so linked or grouped.

In one preferred implementation of the method, reduced manual operatorsetup limits data entry significantly from that previous. For example,depending on the instrument, its operating configuration, operationalmodes and, perhaps other factors, manual data entry can be limited toscan size, e.g. pre-scan size, operational mode, where applicable, andscan force or speed, once again where applicable and the estimated timeto finish the operation. It should be noted that in the case where eventhese parameters can be addressed in an automated fashion, the presentinvention contemplates in such a case the operator simply pressing asingle button, whether physical or on a computer display. Where such“one touch” operation is possible, instrument setup, including anyoperating parameter determination and tuning, is completely automatedpreferably both prior to and during actual operation.

After any manual data entry is completed, an automatic tuning procedurecan be performed, such as where it is desired to operate the instrumentin a desired mode requiring such tuning. For example, where themeasurement instrument is an AFM, automatic tuning can be done where theAFM is going to be operated in an oscillatory mode, such asTappingMode™. In one preferred implementation, automatic tuning iscarried out to determine a resonant or natural frequency of themeasurement instrument cantilever, as well as the drive signalinformation such as drive frequency, amplitude and drive phase, takinginto account any relevant factors that might affect such determinationduring actual operation.

During or after any automatic tuning carried out, obtaining, selectingand determination of values of at least a plurality and preferably aplurality of pairs of operating parameters are obtained, determined orotherwise selected. Where determined, the setting can be calculated,where obtained, the setting can be looked up, such as from a datastorage location, including that which is part of a lookup table, andwhere selected, the setting chosen can be based on a comparison,relativity, or the like.

During or after this procedure, the value of one or more operatingparameters can be tuned or optimized. For example, in one preferredimplementation, automatic gain optimization is performed to set integralgain (I-gain) and proportional gain (P-gain) to an optimum value. Suchoptimization can be based on one or more of noise, amplitude, stepresponse of the system or tracking quality and can be based on all ofthese if desired. The automatic gain optimization is performed at zeroscan size that greatly assures the minimized damage on the tip andsample.

A pre-scan can be carried out in addition to or as part of tuning andoptimization. In one preferred implementation, a pre-scan of the sampleis done to optimize at least a plurality of gain, setpoint value,Z-limit (dynamic range of the Z-piezo), amplitude, e.g. free air tappingamplitude, scan size, scan rate, number of scan lines, number of pixelsscanned per line, digital-to-analog resolution, Z-center position, etc.In one preferred implementation all of these are tuned or optimizedduring the pre-scan.

In a preferred pre-scan implementation, a tracking metric indicative oftracking quality is carried out to determine whether tracking isacceptable. Where unacceptable, the value of one or more operatingparameters, such as scan speed or rate, setpoint, drive frequency, driveamplitude and/or gain is adjusted to see if tracking quality improves.If not, additional adjustment is performed until selection is made ofthe operating parameter value at which tracking quality in thatparticular instance is highest based on the tracking metric. In rarecircumstances, after the self-optimization has done its best and thetracking quality is still poor, an error message will be displayed tothe user to indicate the untruthfulness of the output data.

The above-mentioned procedures have been successfully implemented withVeeco's Multimode® and Dimension® 3100 AFM microscopes. They have beentested with Tapping Mode in air on various kinds of samples includingheight standards, CD stampers, Si wafers, and some polymer samples witha successful rate higher than 95%.

These and other features and advantages of the invention will becomeapparent to those skilled in the art from the following detaileddescription and the accompanying drawings. It should be understood,however, that the detailed description and specific examples, whileindicating preferred embodiments of the present invention, are given byway of illustration and not of limitation. Many changes andmodifications may be made within the scope of the present inventionwithout departing from the spirit thereof, and the invention includesall such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart illustrating a general method of automating SPMsetup according to the preferred embodiment;

FIG. 2 is a schematic diagram of a conventional AFM;

FIG. 3 is a schematic diagram of conventional optical deflectionmonitoring system of an AFM;

FIG. 4 is a schematic diagram illustrating a probe of an AFM beingoscillated in torsion;

FIG. 5 is a schematic diagram of an alternate AFM setup;

FIG. 6 is a flow chart illustrating an alternate automating SPM setupmethod according to the preferred embodiments;

FIG. 7 is a user display interface according to the preferredembodiments;

FIG. 8 is a flow chart illustrating a method of determining the naturalresonance frequency of a probe according to the preferred embodiments;

FIG. 9 is a flow chart illustrating a method of placing the AFM in aSafe Mode, according to the preferred embodiments;

FIG. 10 is a flow chart illustrating a method of automatically adjustinggain according to the preferred embodiments;

FIG. 11 is a flow chart illustrating an alternate method ofautomatically adjusting gain according to the preferred embodiments;

FIG. 12 is a flow chart illustrating a method of pre-scanning a sampleaccording to the preferred embodiments;

FIGS. 13A and 13B are schematic top views of a sample, illustrating twoimplementations of relative raster scanning motion between the probe tipand sample;

FIG. 14 is a flow chart illustrating a method of performing gainadjustment according to the preferred embodiments;

FIG. 15 is a flow chart illustrating a method of automatically settingsystem gains using automatic gains tuning according to the preferredembodiments;

FIG. 16 is a flow chart similar to FIG. 15, illustrating an alternatemethod of gains tuning;

FIG. 17 is a flow chart illustrating determining system setpointaccording to the preferred embodiments;

FIG. 18 is a flow chart illustrating a method of self-optimizing asystem setpoint according to the preferred embodiments;

FIG. 19 is a flow chart illustrating a method of setting scan rate andscan speed according to the preferred embodiments;

FIG. 20 is a flow chart illustrating another method of setting scan rateaccording to the preferred embodiments;

FIG. 21 is a flow chart illustrating a method of optimizing AFMoperation using tracking analysis, according to a preferred embodiment;

FIG. 22 is a schematic top view diagram of a sample illustratingbi-directional scanning as part of tracking analysis;

FIG. 23 is a view similar to FIG. 22 illustrating an alternate scanningpattern;

FIG. 24 is a flow chart illustrating a method of setting and preferablyoptimizing gains during the pre-scan, according to the preferredembodiments;

FIG. 25 is a schematic view of a section of a sample illustrating abreak in the interaction between a tip and the sample on retrace;

FIG. 26 is a graph of the output generated by TMR for the sample shownin FIG. 25;

FIG. 27A is a graph of an offset that may occur during collecting traceminus retrace data;

FIG. 27B is a plot of TMR corresponding to FIG. 27B, illustrating alimitation of TMR;

FIG. 28 is a flow chart of a preferred tracking qualification algorithm;

FIG. 29 is a more detailed flow diagram of a preferred trackingqualification algorithm;

FIG. 30 is a plot of consecutive pixel difference data, according to thepreferred embodiment;

FIG. 31 is an assessment plot of the slope samples, according to thepreferred embodiment;

FIG. 32 is an assessment plot similar to FIG. 31, illustrating tracedescending and retrace ascending data;

FIG. 33 is plot comparing ascending slopes and descending slopes; and

FIG. 34 is a flow chart of an alternate embodiment of the trackingqualification algorithm, according to the preferred embodiments.

DETAILED DESCRIPTION OF AT LEAST ONE PREFERRED EMBODIMENT

FIG. 1 presents a flowchart 30 illustrating a preferred method of theinvention used to automate operation, particularly setup, of a probetype measurement instrument 32 employing, for example, a scanning stylusor tip, depicted schematically in FIG. 2. The measurement instrumentmethod of the invention advantageously simplifies measurement instrumentsetup by reducing the number of setup parameters a user must estimateand manually input before using the measurement instrument. For example,the method of the invention beneficially eliminates virtually all of thetrial and error typical of the past when setting up a scanning probetype measurement instrument.

With continued reference to FIG. 2, one type of probe type measurementinstrument 32 for which the method of the invention is particularly wellsuited is a type of Scanning Probe Microscope (SPM) called an AtomicForce Microscope (AFM) 34. The AFM 34 has a head 36 that preferably ismovable in at least one direction or axis relative to a sample 38disposed in a cell, e.g., a fluid cell or on a sample holder 40. Thehead 36 includes a probe mount 42 that releasably accepts a probe 44including a cantilever 46 that typically is also equipped with a tip 48(i.e., stylus) at or adjacent its free end. To obtain measurement dataduring AFM operation when analyzing the sample 38, deflection of thecantilever 46 interacting with the sample 38 is detected using adeflection monitoring system 50. A controller 76 preferably usesdeflection information as feedback to determine whether to change oradjust the relative position between the tip 48 and sample 38 such as bymoving one relative to the other.

FIG. 2 illustrates an optical-type deflection monitoring system 50 whichincludes a beam emitter 52 that outputs a beam 54 that reflects off thecantilever 46 against a sensor arrangement 56 that preferably includesat least one beam detector 58. The beam emitter 52 typically is a laser60, such as a diode laser, and the beam detector 58 typically is a photodetector 62, preferably a photodiode. Often times, a plurality of photodetectors 62, usually four, is used to enable precise measurement of thelocation of the reflected component 64 of the laser beam 54 on the beamdetector 58 in measuring deflection of the cantilever 46.

Deflection measurement data 80 is provided to the controller 76, whichpreferably processes it before outputting it as output data 74,typically by processing the deflection measurement data 80 as feedbackto determine a drive signal 78 based on an oscillation setpoint (e.g.,amplitude, phase or frequency) used to adjust the relative positionbetween the tip 48 and sample 38. For example, as is shown in FIG. 2,feedback from deflection data 80 is used to generate at least one drivesignal 78 that drives at least one actuator, such as a piezoelectricactuator, to change relative tip 48 sample 38 position. While theparticular AFM embodiment shown in FIG. 2 feeds the drive signal 78 to ascanner actuator assembly 66 underlying the sample 38 to move the sample38 relative to the tip 48, it is contemplated that the AFM 34 can beconfigured to provide the drive signal 78, or an additional drive signal(not shown), to drive a scanner actuator assembly (not shown) of thehead 36 such as to move the tip 48 relative to the sample 38. Moreover,processing of the acquired deflection signals can be implemented inanalog with an RMS-to-DC converter, a comparator and a gain stage (PI,for example), or even more preferably, the processing can be performedentirely digitally, including the gain stages.

In preparation for AFM 34 setup and use, a probe 44 is installed on theAFM head 36, a sample 38 is placed in its holder 40, the cantilever 46is aligned relative to the laser 60, and the photodiodes 62 of the beamdetector 58 are also aligned. In practicing the measurement instrumentsetup method 30 of the invention illustrated in FIG. 1, an AFM operator(not shown) enters a reduced set of initial setup data 68 as compared towhat was previously done following conventional setup procedures. Thisadvantageous aspect of the method of the invention alone significantlyspeeds setup, for example, because no more than about 15% of the setupdata is manually entered as compared to before. Once initial manual dataentry 68 is completed, automatic setup value determination 70 isinitiated to determine the rest of the setup values, at least some ofwhich previously needed to be entered manually. These automaticallydetermined setup values are then used during AFM operation 72 to analyzethe sample 38 from which output data 74 is obtained.

If desired, the output data 74 can be further analyzed, manipulated,processed, etc. However, as is normally the case, the output data 74 canalso be used to make an image of the sample 38. For example, dependingon its format, etc., the output data 74 can be outputted as an image orin an image format. Such an image can be displayed, such as on a monitoror the like, or printed out. The output data can also be stored,including in an image format or the like, such as for subsequentreference, comparison, additional processing, analysis, etc.

While the method of the invention is particularly well suited forautomating setup of an AFM 34, it is also well suited for automatingsetup of other types of probe type measurements. For example, in onemethod implementation, the method discussed above in conjunction withFIGS. 1 and 2, as well as those method implementations discussed hereinbelow, can be adapted for use in automating setup of another type ofSPM, namely a Scanning Tunneling Microscope (STM).

This also holds true for other types of scanning stylus or probe typemeasurements as well as for their different modes of operation. Forexample, FIG. 3 illustrates an AFM 34 a suitable for use with the methodof the invention that is configured for operation, for example, in anon-contact, non-oscillatory mode such that interaction between the tip48 of the cantilever 46 and the sample (not shown in FIG. 3) is indirectand typically either attracts or repels. The AFM 34 a differs from thatshown in FIG. 2 in that the reflected beam component 64 is, in turn,reflected off of an optical element 82, e.g. a mirror or the like,before the second reflected component 84 irradiates one of a pluralityof side-by-side photo detectors 62 labeled A and B.

FIG. 4 illustrates another suitable AFM 34 b operating in an oscillatingmode known as torsional deflection mode with, for example, the tip 48 ofthe torsional cantilever 46′ being scanned along the sample (not shown)in a transverse direction as shown. Its deflection monitoring system 50′directs a beam 54, such as a laser beam, that reflects off the topsurface 86 of the cantilever 46′ adjacent its free end, preferablygenerally overlying the tip 48 as the probe is driven to oscillate intorsion. As the cantilever is scanned in a sideways direction along thesample (not shown) changes in the torsional oscillation of thecantilever 46′, i.e. torsional deflection, causes the reflected beamcomponent 64 to change the location of the spot 88 where it impingesagainst at least one of four photo detectors 62 arranged in the fourquadrant beam detector array 90 depicted in FIG. 4. In one embodiment,Z-direction cantilever deflection, i.e., deflection toward or away fromthe sample, can also be measured.

FIG. 5 depicts still another AFM 34 c that is well suited for automatedsetup employing a method in accordance with the present invention. Thecantilever 46 of the AFM 34 c is driven in an oscillatory mode, such asTappingMode™, where amplitude, A, phase, φ, and possibly frequency, ofthe cantilever 46 are monitored and analyzed, such as by AFM controller76. During operation, for instance, phase related feedback from thecantilever can be used along with cantilever deflection feedback fromthe deflection monitoring system can be used to adjust or otherwiseregulate driving of the cantilever in a desired manner. For example,such feedback can be used to adjust the amplitude, phase, frequency,etc. of a drive 92 used to oscillate the cantilever 46 during operation.

Overall, the method of the present invention provides significantadvantages over conventional manual setup procedures used in the pastfor these and other types of measuring instruments. Not only does themethod of the present invention significantly speed up setup, it alsoprovides more consistent measurement instrument results, increasesmeasurement instrument uptime, reduces cantilever and tip damage duringsetup, all while making it easier for veteran and novice users alike tosetup and quickly, consistently and repeatably use the measurementinstrument no matter what the application, sample type, instrument type,mode of operation, cantilever configuration, etc.

FIG. 6 illustrates a currently preferred measurement instrument setupmethod implementation 30 a that includes additional method steps 96-102that further define the automatic setup value determination step 70 ofthe method shown in FIG. 1. These steps, also collectively grouped underreference numeral 70 a, include an automatic parameter tuning step 96, apre-scan setting determination step 98, an automatic gain adjustmentstep 100, and a pre-scan step 102, which also preferably is configurablein a manner that helps further optimize at least some of the setupparameters.

While these steps can be implemented in the method as needed, preferablyall are employed in the currently preferred method implementation shownin FIG. 6. As a result, virtually all, if not every single one, of theinitial measurement instrument operating parameter settings needed tobegin operation are not only automatically determined before operationbegins but preferably also optimized, to at least some degree, along theway so as to help improve operational speed, increase scanningefficiency, maximize scan quality and resolution, minimize tip and/orsample damage, all while increasing repeatability. In addition, asdiscussed in more detail below, at least a plurality of these steps canalso be implemented in at least an as-needed basis during measurementinstrument operation to dynamically self-optimize operation bycontinuing to adjust the value or values of one or more measurementinstrument operating parameters.

Referring additionally to FIG. 7, in carrying out the methodimplementation depicted in FIG. 6, an operator provides initial settingsfor at least one of scan size 104, scan force versus high speed 106(depending on, for example, the type of sample), and/or measurementinstrument operation mode 108. For example, FIG. 7 depicts a preferredbut exemplary data entry screen or window 116, ideally implemented insoftware and visually displayed to the operator, such as on-screen on acomputer monitor. Alternatively, another switch of any kind of form,toggle or slide bar, can be added to control the imagequality/resolution (the number of scan lines in each image) vs. imagingspeed. The more scan lines in one image, the longer time it takes tofinish. Alternatively, another display window can be added to inform theusers of maximum imaging time required when they change the settings ofthe switches.

The initial settings data entry screen 116 is configured to allow theoperator to manually input an initial value preferably for no more thanthree setup parameters. In the preferred data entry screen configurationdepicted in FIG. 3, a Scan size numerical value 104, preferably in μm,is manually entered in an on-screen text box 110 if no values areentered by the user, a default value, for example, 1 μm will be used, achoice is presented to select between a High Speed and a Low Force probescanning parameter 106 selected by manipulating the position of anon-screen toggle switch 112, an alternative way is to use a slide barcontrol so that the user can have more choices on Speed and Forcecombinations, and, depending on the capabilities, e.g., modes, of themeasurement instrument, a Scanning Device Mode 108 also is manuallyselected, such as via a drop down selection menu 114.

Of course, other ways, arrangements, configurations, etc., can beutilized to facilitate entry of such initial parameter data. Forexample, combo-boxes, check boxes, radio buttons, drop down menus, orthe like can be used, where suitable, to facilitate data entry for anyof these initial setup parameters.

Where the measurement instrument has only a single mode of operation orhas multiple but sufficiently similar operating modes, e.g., such as isthe case for an STM, the Scanning Device Mode 108 may not be needed.Where this is indeed the case, Scanning Device Mode 108 can either bedisabled or eliminated. Additionally, in the case where sample size isfixed or an effective scan size is established, it also may not benecessary to manually input Scan size 104 each time.

After initial setup is completed, the operator initiates automatic setup94 by pressing the “GO” button 118, preferably using a selection device,such as a mouse or a computer keyboard. Thus, with just one touch of asingle button, measurement instrument parameter setup preferably alongwith setup optimization is initiated, making operation both simple andfast. Alternatively, an “Abort” or “Stop” button can be added to cancelthe operation at any time.

Referring additionally to the flowchart 120 shown in FIG. 8, theautomatic tuning step 96 is carried out to determine an operationalfrequency of the probe, as well as the drive signal (frequency,amplitude and phase). In a preferred implementation of this method step,automatic tuning 96 is carried out to determine a cantilever resonantfrequency 124 such as, for example, the natural frequency of thecantilever. However, it should also be recognized that this method stepmay not always be required. For example, it may not be needed forcertain types of measurement instruments and for certain operationalmodes. For example, with regard to AFMs, the automatic tuning step 96may only be needed when operating in an oscillatory mode, including inparticular, TappingMode™. In the currently preferred implementation ofthis method, the automatic tuning step 96 is performed for setting up anAFM that is going to operate in TappingMode™ where the tip of acantilever being oscillated at or near a resonant frequency is going tointermittently interact with the sample.

In one preferred implementation of this method step, the cantilever isfreely excited into oscillation 122 and the damping of its oscillationsafter ceasing excitation can be measured or analyzed to determineresonant frequency or a harmonic thereof 124. When operating inTappingMode™, for example, the cantilever of the measurement instrumentis oscillated at frequencies near the resonant frequency until theresonant frequency is determined. This typically can be done in free airand in liquid, depending on the intended application. If desired,cantilever Q can also be determined in determining resonant frequencyand can also play a role in resonant frequency determination, as well asimpact the speeds at which the AFM is capable of operating. Ifavailable, another way of determining or measuring resonant frequencycan also be used in carrying out this method step.

Referring additionally to the flowchart 126 shown in FIG. 9, regardlesswhether an automatic tuning step 96 is employed, automatic determinationof at least one value for at least a plurality of pairs of parameters iscarried out in the pre-engagement determination settings method step 98.This step 98 involves obtaining or otherwise determining at least one“safe” value for a plurality of parameters required for pre-scanoperation such that the value used as the initial setting reduces andpreferably minimizes the likelihood of tip and sample damage during thepre-scan. This need not be done for parameters already optimized forpre-scan and for parameters which already are set at a suitably safevalue. If desired, checking can be performed on one or more alreadydetermined values to check to see if their value is safe and to adjustit to a safe value if not.

A check 128 preferably is performed to determine whether the measurementinstrument came pre-equipped with a safe mode feature previouslyintended to help minimize tip and sample damage during manual operatorsetup. Where so equipped, the instrument preferably is then put in safemode 130. Where the safe mode sets certain parameters to suitably safevalues, the present pre-engagement settings step 98 contemplates beingat least configurable so as to be able to use or otherwise takeadvantage of the values parameters are set to in safe mode. In onepreferred embodiment, the pre-engagement settings step 98 utilizes thebenefits of such a safe mode already built into the measurementinstrument by automatically switching it to the safe mode and utilizingany corresponding safe mode values operating parameters are set to as aresult.

If desired, a check 132 can be performed do determine whether any of thesafe mode parameter values, as well as for any previously determinedparameter value, is suitably safe for use as an initial pre-scan valueor whether the parameter value needs adjustment. To the extent needed,those parameter values in need of adjustment are adjusted 134 to asuitably safe value.

In carrying out pre-engagement settings determination, at least somepre-engagement settings preferably are selected or otherwise obtained136 from a storage location, such as computer memory, flash memory,etc., where they have been pre-stored. Such settings can be part of alookup table, e.g., a data table, (not shown) which is accessed incarrying out this method step 136.

If desired and to the extent necessary, values for other parametersettings can also be determined 138, including by calculation, such aswhere the value of the setting is dependent on some other factor. Forexample, where it is desired to constrain the values of two parametersto a desired ratio, selection of the value of one parameterautomatically determines the value of the other parameter such that theyare in accordance with the desired ratio.

Referring to FIGS. 6 and 9, in one preferred implementation, initialpre-engagement (pre-scan) safe values are set for between ten and twentymeasurement instrument operating parameters. For example, in onecurrently preferred implementation, values for between fourteen andsixteen, typically about fifteen, such parameters are set. These includesetting an initial safe value for at least the following parameters: (a)integral (I) gain, (b) proportional (P) gain, (c) amplitude noise (N),i.e., a noise threshold value, (d) a “back off” percentage, (e) fixedscan size, (f) scan rate, (g) number of scan lines, (h) bi-directionalpre-scan I- and P-gain settings, I_(b) and P_(b), (i) offset voltage,and (j) Z-limit. The safe value need not necessarily be fixed. Rather,it can be a value falling within a safe range of suitable limits betweenwhich it is known to be safe. The value of a particular parameter canalso depend on the value of some other parameter, even if it also mustfall within a safe range of suitable values.

In one preferred implementation, each value is within ±15% of nominal.In another preferred implementation, each value is set right in themiddle, i.e., midpoint, of its outer extents or limits or within 10% ofits midpoint. Depending on whether the operator selects a high speed ora low force pre-scan force setting 106 (FIG. 7), the safe value candeviate in one direction or the other by as much as, for example, 20%from this safe value. For example, where high speed pre-scan is chosen,the safe value for one or more parameters may increase or decrease fromthe low force safe value by as much as 20% for a particular parameter.In contrast, where low force pre-scan is chosen the converse can be trueand preferably, is true for at least one parameter in at least onepreferred method implementation. Thus, a method according to the presentinvention preferably is configurable to select safe values for at leasta plurality of parameters that differ depending on whether low forcepre-scan or high speed pre-scan is chosen.

FIG. 10 illustrates a flowchart 148 of a preferred implementation of anautomatic gain adjustment method step 100 where the I-gain and P-gainare both ramped up 140 while amplitude noise is monitored 142 at a zeroscan size setting. When amplitude noise reaches a certain value orthreshold, gain ramping is stopped 144 and I-gain and P-gain are bothset at a value based on the noise value when gain ramping stopped 146.In a currently preferred implementation, gain ramping is stopped 146when the amplitude noise approaches, e.g., is within 5%, or reaches theonset of feedback loop oscillation. Feedback loop oscillation onset isdetected when the amplitude noise reaches 200% of the normal level undercertain parameter settings. For example, in one preferredimplementation, I-gain and P-gain are both ramped up by increasing eachone of their values until a noise threshold is reached. At that point,the value of the I-gain and P-gain are each set at their respectivevalue when the threshold is reached. Thereafter, the I-gain and P-gainvalues at the time the threshold is reached are then backed off, such asby reducing them, for example, at least 3% and preferably no more than15%, from their respective value at the time the noise threshold wasreached.

FIG. 11 is a flowchart 150 depicting a more detailed and preferredimplementation of the gain ramping step 140, the amplitude noisemonitoring step 142, and the gain ramp stopping step 144 of theautomatic gain adjustment method 100 depicted in FIG. 10. Initially, inpreparation to ramp up the gains 140, the I-gain and P-gain are set todifferent values 152. In addition to being unequal in value, the gainvalues are also set to a desired fixed ratio 154 that preferably ispredetermined.

Thereafter, amplitude noise is determined 156, such as by being sensed,calculated or otherwise measured. For the particular noise levelproduced at a particular gain or gains setting, a check 158 is made todetermine whether feedback loop oscillation is beginning. If not, bothgains are ramped 160, preferably by being changed, e.g., increased,converged, diverged, etc. and amplitude noise is once again determined156. If the onset of feedback loop oscillation has been reached, a noisethreshold is set to the value of the amplitude noise 162 and gainramping is stopped 164.

While amplitude noise preferably is determined in step 156 before anygain ramping occurs in step 160, it should be noted that this order canbe reversed if desired. In addition, it should be noted that feedbackloop oscillation onset includes not only the case when feedback looposcillation is beginning or about to begin, it also includes the casewhere it has already begun for some reason.

To provide an extra safety buffer to further minimize the possibility oftip and sample damage, at least one of the gains, and preferably both ofthe gains, are reduced 166, i.e., backed off, from the gain value orvalues when the noise threshold 162 was reached. Each of these reducedgain values are then set as the initial pre-scan gains 168 and thecorresponding noise level of these gains also preferably is also kepttrack of 170, such as by being stored in memory or the like, therebymaking it available for reference during the pre-scan. This noisereference preferably advantageously is usable during pre-scanning as alimit by which to ensure initial parameter value settings will nottrigger feedback loop oscillation during actual measurement instrumentoperation.

A preferred implementation of the pre-scan step 102 (FIG. 6) isillustrated by the flowchart 172 of FIG. 12. If any pre-scan parameterswere not previously set, they can be done so in step 174. In onepreferred method implementation, certain pre-scan parameters are set-up174, the tip is engaged with the sample and the pre-scan is performed176, amplitude error or RMS height are monitored 180, the maximumamplitude error and/or height value is stored 182, gain adjustment, tothe extent any is needed, is performed 184, until completion of thepre-scan 178. Besides gains, other parameters can be adjusted in 184 andinclude the Z-limit, setpoint, scan rate, height channel display datascale, etc. When the pre-scan is completed, the measurement instrumentis ready for actual operation such that operational parameters,including gains, have been optimized in a manner that maximizes imagesample quality during actual operation.

The pre-scan setup parameter step sets any parameters not previously setand therefore may not always be needed in cases where all pre-scanparameters were previously set. However, in the preferred methodimplementation depicted in FIG. 12, one or more of the scan size,operating setpoint, and scan rate are set to a fixed value preferablydetermined to provide sufficient information during the pre-scan tooptimize the desired parameters while minimizing the time it takes tocomplete the pre-scan. Certain scanning modes preferably are also set,including setting scan resolution to its lowest available mode that willstill achieve these goals as well as switching the measurementinstrument to bi-directional scanning mode.

The fixed value settings are at least initial values as the method ofthe invention contemplates being capable of automatically changing oneor more of these settings during pre-scanning preferably to optimizeeach such setting. Additionally, those values that are set beforeengaging the tip to the sample and beginning the pre-scan areautomatically set and can be obtained from memory storage, a computerreadable disk, or the like, and can be read from a lookup table or datatable, if desired. Such memory storage, computer readable disk, etc. canbe located onboard the measurement instrument controller or be part of aseparate computer having a processor configured to carry out one or moreof the steps of the method of the invention. Such a computer preferablyis linked, either directly or wirelessly, to the measurement instrument,preferably to its controller, and can be part of a computer network ifdesired. Moreover, if desired, such a computer can be remotely locatedand connected via a telephone link, via the Internet, via FTP, or viaanother communication arrangement.

Setting the measurement instrument to low resolution mode forbi-directional scanning minimizes the amount of time it takes tocomplete the pre-scan and move on to actual measurement instrumentoperation. Where a measurement instrument has more than one lowresolution mode, the lowest resolution mode that provides sufficientinformation during scanning to optimize the desired parameters optimizedduring the pre-scan is chosen. The same is also true for any of theother pre-scan parameters.

Each parameter set prior to the pre-scan preferably is set with aprimary goal of minimizing the overhead of performing the pre-scan sothat it is completed as quickly as possible but remains effective.Another primary goal of the pre-scan is to optimize the values orsettings of certain measurement instrument operating parameters tomaximize image quality during actual measurement instrument operation.In seeking to achieve this goal, force is limited so it remains lowduring bi-directional scanning to limit tip damage because tip damagetypically results in reduced image quality. To help achieve this goalwhile simultaneously minimizing the time it takes to complete thepre-scan, applicable pre-scan parameter settings limit the pixels perscan line and the number of scan lines to less than the pixels per scanline and number of scan lines minimally required to obtain a standardimage of the same sample. For example, where a standard image of aparticular sample is 512 pixels per line and 512 scan lines, pre-scanlimits the pixels per line to no more than 10% of the correspondingstandard image value and the number of scan lines to no more than 10% ofthe corresponding standard image value.

During the pre-scan 176, the probe is engaged with the sample so as tointeract with the sample. Referring additionally to FIGS. 13A and B, theprobe scans or rasters along the sample area 38 in a zig-zag pattern. Asis shown in FIG. 13, to reduce pre-scan time, the tip (not shown)interacts with the sample 38 as it travels making a single scan pass 186a given distance in one direction. In the present example, the scan pass188 is in a horizontal direction along the width of sample area 38. (Thereference to a horizontal direction is for clarity in discussing thedrawings, but is not intended to imply a specific required scandirection relative to the sample. The scan pass may be oriented in anydirection that is substantially in the plane of the sample.)

Once a scan pass 188 is completed, the probe is jogged in a transversedirection for a section 190 based on the spacing dictated by theparameter setting the number of scan lines for the pre-scan. Thereafter,another scan pass 188 is made in a direction substantially opposite tothe preceding scan pass 190. Scanning proceeds accordingly in such aback and forth manner until the scan size 104 (FIG. 7) of the samplearea 38 is pre-scanned. Note that this raster scan can be created bymoving the probe, the sample, or any combination thereof. The onlyrequirement is that relative translation be created between the probeand sample.

An alternative version of raster scanning in FIG. 13B. In this version,the scan passes are at a slight angle from the horizontal direction. Theforward scan pass 186 traverses a horizontal distance substantiallysimilar to the scan size, but also moves a small amount in the verticaldirection (as one views the page) in parallel with the horizontalmotion. The net result is a slightly angular scan pass. Next the reversescan 190 is made in substantially the opposite horizontal direction, butalso with a small vertical motion. The amount of vertical motion forforward and reverse scans is determined by the vertical scan size andthe number of lines in the image. For example, a 1 μm×1 μm scan areawith one hundred forward scan passes 186 and one hundred reverse scanpasses 190 would have a vertical motion in each scan pass of 1 μm/200lines=0.005 μm=5 nm. The resulting off-axis angle would be roughly 0.3degrees. (This example is for illustration and is not intended to limitthe number of scan lines or amount of off-axis motion.)

Note that the vertical separation between scans in FIGS. 13A & B arehighly exaggerated for clarity. In practice, the forward scan pass 186and reverse scan pass 190 cover substantially similar regions of thesample. In practice the requirement is that substantially similarfeatures of the sample surface are measured in both the forward scanpass 186 and reverse scan pass 190 such that the measured data of thesimilar features can be compared. Further, for the purposes of thisapplication, forward scan pass 186 and reverse scan pass 190 should beconsidered to be in “substantially opposite directions,” despite thesmall off-axis angle differences.

During pre-scanning, amplitude error or RMS height is monitored 180 andeach time a new maximum value is reached, it is stored. Using thisinformation, adjustment of at least one and preferably both of theI-gain and P-gain is performed after pre-scan. Alternatively, gainadjustment can also be optimized in real-time in an ongoing mannerduring pre-scanning.

Where tracking analysis is performed, at least a plurality of thehorizontal scan passes 186 is modified so each is bi-directional, i.e.,such that the scan travels back and forth at least once along the samehorizontal scan line, as discussed in more detail below and exemplifiedin FIGS. 22 and 23, instead of the unidirectional horizontal scan passes186 depicted in FIG. 13. While substantially the entire outer surface ofthe sample 38 may be pre-scanned as shown in FIG. 13, it is more typicalthat the pre-scan size be substantially less than the surface area ofthe outer surface of the sample.

FIG. 14 illustrates one preferred implementation for performing gainadjustment 184. In performing gain adjustment 184, the recorded maximumerror/height value is compared against an amplitude noise level,preferably the level corresponding to the maximum. Thereafter, the gainsare adjusted in step 194 based on these parameters.

Preferably, the gains are adjusted in step 194 as needed to achieve afixed maximum error/height—noise level ratio. This is because therelationship between the gains and maximum error/height is generallylinear where the scan rate, scan size and setpoint are fixed. FIG. 15illustrates a currently preferred implementation of a method 196 forsetting the gains that includes automatic gains tuning that takes placebefore pre-scanning the sample as well as any automatic gains tuning orself-optimizing adjustment that is performed during pre-scanning. I-gainand P-gain are set in step 198. At first, they are preferably set to aninitial safe value. For example, as previously discussed, bothpreferably are set so they are different from each other. In at leastone preferred embodiment, the values chosen for the gains are set to adesired predetermined ratio that preferably is fixed.

In ramping up the gains 200, the value of each gain is incremented by acertain amount. As is shown in FIG. 15, the I-gain is incremented by ΔIand the P-gain is incremented by ΔP. Thereafter, the amplitude noiselevel is measured 202. If the noise level exceeds a certain threshold orthe value of the I-gain exceeds a certain pre-determined maximum 204,both gains are reduced by a certain amount 206. For example, as isdepicted in FIG. 15, where either case is met, the I-gain is reduced byan amount, δI, and the P-gain is also reduced by a corresponding amount,δP. If no noise threshold or gain maximum is reached or exceeded, gainramping continues and each gain is incremented by a correspondingincremental value in step 200.

In each case, δ preferably is a “back off percentage;” a multiplierwhich reduces both gains by a desired predetermined percentage. Thispercentage is selected based on routine testing and experimentation toback each gain off enough to provide a safe buffer that they cannotexceed during actual measurement instrument operation. This safetybuffer ensures that the measurement instrument simply cannot operate atany gain that produces feedback loop oscillation. This advantageouslylocks in gains so they always stay at a safe value or within a safevalue range. The not-to-exceed threshold gains that result areparticularly advantageous where self-optimizing automatic gainadjustment is performed during imaging of the sample 38 during actualmeasurement instrument operation.

After each gain is backed off from its value when the noise threshold ormaximum I-gain was reached or exceeded in step 204, the I-gain andP-gain are set in step 210 at the backed off value calculated in step206. Thereafter, another automatic gain optimizing loop 208 is initiatedto further tune and self-optimize gain. Once again, gains are ramped instep 212 up by incrementing the gains a corresponding desired amount,ΔI′ and ΔP′, which differs from the increment values previously employedin step 200 of the initial gain tuning loop 197. Preferably, ΔI′ and ΔP′are each smaller than ΔI and ΔP, such as to fine tune and more preciselyoptimize gain.

Amplitude noise is recorded in step 214 and it is compared against athreshold and I-gain with a maximum I-gain value in step 216. If neitheris exceeded, gain ramping once again resumes at step 212. If eithervalue is exceeded, I-gain is then compared in step 218 to see if it isgreater than a predetermined minimum gain value, I_(min). If it is not,the offset is adjusted in step 220 and the whole automatic gain tuningprocess is started over returning to initial gain tuning loop 197.

The scan size is set to zero when doing the auto gain adjustment. Thereason for changing the X-offset is to prevent that the tip lands on aspecific “bad” region on the sample 38, which gives a high amplitudenoise even at very low gain settings. Note, that the X-offset is usuallya smaller value than the half of the scan size from the user input. TheX-offset will be set back to zero after the auto gain adjustment.

However, if I-gain is greater than the predetermined minimum, I_(min), apre-scan gain-tuning loop 222 is initiated with amplitude noise at thepresent P-gain and I-gain value being recorded in step 224. This clearsthe way for pre-scanning to proceed, including any additional pre-scanpreparations not shown in FIG. 15, using the final I-gain and P-gainvalues from loop 208 as initial gain values in loop 222.

Once pre-scanning begins 226, the maximum error and maximum amplitudelevel are obtained in step 228. In a subsequent step 230, I-gain andP-gain preferably are both calculated based thereon. The gains can bedetermined used either a look-up table or an equation fitted by theexperiment results. For example, one of the possible equation can beused is as following:Gain factor[a*ln(maximum error)]−b

From experiment results, the preferred values of “a” and “b” are about0.35 and 1.

This loop preferably executes in this manner, and can do so recursively(not shown), until pre-scanning is finished 234. When finished, thefinal I-gain and the P-gain are set 232 and preferably are both based onthe highest maximum error and/or maximum amplitude obtained in step 228.It is these final gain settings that will be used during actualmeasurement instrument operation in actual imaging of the sample 38.

FIG. 16 depicts another preferred automatic gains tuning method 236 thatshares some similarities to the method shown in FIG. 15. For example,the method 236 illustrated in FIG. 16 includes an additional automaticgains tuning loop 238 that takes place just before the pre-scan tuningloop 222 is initiated. Additionally, gain ramping in at least one ormore of the loops includes incrementing at least one of the gains basedon a multiplier as well as preferably doing the same with the othergain. Moreover, in step 206′ not only are I-gain and P-gain backed off,but the value, I, of the I-gain is also recorded, e.g., stored. Furtherdifferences are discussed in more detail below with regard to thismethod that, among other things, sets the initial pre-scan I-gain valueto the highest I-gain value obtained from the I-gain values outputted bythe three automatic gain tuning loops 196, 208 and 238 employed in thepresent method 236.

For example, in left-hand side loop 197, P-gain is incremented duringgain ramping 200′ using a multiplier, a, that is multiplied with anI-gain value, preferred its value at the time the P-gain is furtherramped. While coefficient, a, can be selected so the resultant productof multiplication with the I-gain value, i.e., a*I, can be added to thecurrent or prior P-gain value, it preferably is determined such that themultiplied resultant product, a*I, instead replaces P-gain. A similarmethod of determining P-gain during ramping 212′ is performed in themiddle loop 208, except a different coefficient, b, is used as themultiplier, and in the right-hand side loop 236, except coefficient, c,is used as the multiplier.

In the right-hand side loop 208, once the noise threshold or I_(max) isexceeded 216, both gain values are backed off and the I-gain value isstored as variable I′. If desired, I′ can be set at the I-gain value,e.g., the maximum I gain value, prior to being backed off and reduced instep 240.

Both I-gain and P-gain are set to their backed off values in step 242before the right-hand side loop 238 is initiated. Gain ramping 244 isperformed and amplitude noise is obtained 246 before determining whetherthe noise threshold or I_(max) has been exceeded 248. If that is not thecase, gain ramping 244 continues on. If either of these values isexceeded, I-gain and P-gain are backed off in step 250 and I-gain isalso stored as I″ in a manner corresponding to step 240.

Thereafter, I-gain is set 252 at the value of the maximum I-gain, i.e.,the greatest of I, I′ and I″, obtained from each of the three processingloops 196, 208 and 238. If the maximum I-gain determined in step 252 isgreater than a threshold minimum I-gain, I_(min), per step 218, then thepre-scan gains tuning loop 222 is initiated. Otherwise, the offset ischanged, e.g., moving the tip to another area within the sample 38, andthe whole automatic gains tuning method 236 is executed all over againfrom the beginning.

FIG. 17 illustrates a method 254 of setting the measurement instrumentoperating setpoint, S_(p), in preparation for pre-scan. A systemsupplied setpoint factor, F_(s), is obtained or otherwise determined instep 256 before it is used in determining the setpoint in step 258. Asis discussed in more detail below, the setpoint, S_(p), ultimatelyobtained may well be provisional as it may be subject to adjustment,e.g., automatic optimization, which can be performed along withautomatic gain tuning as well during the pre-scan.

FIG. 18 illustrates a currently preferred implementation 260 of theoperating setpoint determination method 254 depicted in FIG. 17. In step262, the setpoint factor, F_(s), is set to be greater than zero, if notalready the case, in step 256. Thereafter, the operating setpoint,S_(p), is calculated in step 264 as the result of the followingequation:S _(p) =F _(s) ×E _(max)

where:

S_(p) is the provisional operating setpoint setting,

F_(s) is the setpoint factor, and

E_(max) is a maximum error.

E_(max) preferably is the maximum error signal (e.g., amplitude)obtained, for example, in step 182 of the method depicted in FIG. 12and/or in step 228 of the methods depicted in FIGS. 15 and 16. Thesetpoint, S_(p), is designated as provisional because it can be alteredas a result of application of tracking control before actual imagingoperation begins as discussed in more detail below.

Where the measurement instrument is being setup for oscillatory modeoperation, namely TappingMode™ operation, operating setpoint relatedsetup further includes a free cantilever oscillation amplitude value,A_(f) or A_(g), which is automatically obtained, such as from a lookuptable, data table, or other data storage arrangement, or determined,such as by calculation or the like. The value obtained, namely eitherA_(f) or A_(g), is automatically selected in carrying out the setpointdetermination method depending upon whether the operator previouslymanually selected the “High Speed,” i.e., fast (FIG. 7), or “Low Force,”i.e., gentle (FIG. 7), operational mode. For example, A_(f) is used whenthe “High Speed” operational mode is manually selected and A_(g) is usedwhen the “Low Force” operational mode is manually selected.

FIG. 19 illustrates a preferred implementation of a method 268 forsetting scan rate and scan speed. For sake of simplicity, only scan rateis addressed because scan rate and scan speed are interrelated accordingto the following equation:Scan Size÷Scan Rate=Scan SpeedSince scan size is previously manually entered 104 (FIG. 7) by theoperator, the above interrelationship between scan rate and scan speedmeans that obtaining the value of one of the other two parameters,namely scan rate or scan speed, automatically results in the value ofthe other one of these parameters being provided.

In determining the value to which scan rate should at least be initiallyset in the preferred but exemplary method 268 depicted in FIG. 19, it isfirst determined in step 270 whether the operator manually selected the“High Speed,” i.e., “fast,” or “Low Force,” i.e., “gentle” pre-scanforce setting. For example, referring once again to reference numeral106 of FIG. 7, if “High Speed” was previously set, such as by operatorselection, decision branch 270 sets the scan rate, or at least causesscan rate to at least initially be set, higher in step 272 than in thecase where “Low Force” was previously set. Thus, if pre-scan force isset to the “Low Force” setting, decision branch 270 sets scan rate, orat least causes scan rate to initially be set, lower in step 274 thanfor the “High Speed” case.

Particularly in the case where the value of the scan rate setting isalso dependent on some other factor such that it can differ for a given“High Speed” or “Low Force” pre-scan operator setting, a check is madein step 276 to determine whether the initial scan rate setting exceeds aknown pre-determined threshold. For example, if the value of the initialscan rate setting made in either step 272 or 274 produces a scan speedtoo great for a given operator set scan size (e.g., per the scan speedequation above) such that the risk of tip or sample damage is too high,the scan rate setting is adjusted accordingly in step 278, preferably byreducing the scan rate setting, before finalizing the setting in step280. However, if the threshold is not exceeded in step 276, no furtherscan rate adjustment is needed and the scan rate setting is finalized.

It should be noted for the “Low Force” case that step 276 may not beneeded, e.g., skipped, where the scan rate is set sufficiently lowenough in step 274 that there is almost no risk of tip or sample damage.Where such is the case, the scan rate is set to a low setting in step274 before immediately preceding to step 280 where the scan rate settingis adopted.

Alternatively, the “High speed”/“Low force” selector can be as a form ofslide bar control, in which the user can choose some intermediate valuesand all the parameters settings related to the “High speed”/“Low force”switch will be obtained from data storage or the like, such as of thetype capable of being retrieved from a lookup table, data table or thelike.

For example, the following tuning free amplitudes and setpoint reductionfactors can be used depending on the higher force or lower forceselector:

Tuning Amplitude (V) Setpoint Factor (%) High speed/Force 2.0 70 ↓ 1.875 ↓ 1.5 80 ↓ 1.0 85 Low speed/Force 0.7 90

While the threshold can be based on calculation, such as calculationsthat estimate tip force or some other aspect of pre-scan force, thethreshold is a value obtained from data storage or the like, such as ofthe type capable of being retrieved from a lookup table, data table orthe like. Such a threshold can be determined based on routine testingand experimentation and can also be based on the type of measurementinstrument. For example, where the measurement instrument is an SPM, thethreshold might be different when the SPM is an AFM as opposed to whenit is an STM.

In addition, while reference numeral 280 refers to finalizing the scanrate setting, it should be recognized that some other characteristic,parameter, function or additional method implementation can cause eventhis “finalized” scan rate setting to be adjusted. For example, as isdiscussed in more detail below, where tracking metrics are analyzed,such as during the pre-scan, the scan rate setting finalized in step 280can be adjusted, preferably optimized, as a result tracking metricsanalysis.

FIG. 20 depicts a currently preferred implementation of a scan ratesetting method 282. Where the “Low Force” or “gentle” pre-scan settingis in effect, the scan rate is set lower 274 than it would be set forthe case where the “High Speed” or “fast” pre-scan setting is in effect.Thereafter, since the scan rate is set sufficiently low enough in thisparticular case that the risk of tip or sample damage is low, the scanrate setting is finalized in step 280.

Where the “High Speed” or “fast” pre-scan setting is in effect, the scanrate is set higher 272 than it would be set for the case where the “LowForce” or “gentle” pre-scan setting is in effect. This scan rate settingcan be adjusted based on subsequent analysis from monitoring probetracking 282 during the pre-scan. Since tracking analysis will notalways have taken place at this point, the scan rate set in step 272 canbe provisional until tracking analysis is performed during the pre-scan.In addition, this method, along with the method depicted in FIG. 19,contemplate an automatic setup method implemented in accordance with theinvention that may lack any kind of tracking analysis performed duringmeasurement instrument setup or which selectively employs trackinganalysis during setup.

Scan rate preferably is adjustable during pre-scan when trackinganalysis is being performed. As is discussed in more detail below, thescan rate at which the best tracking metrics occur preferably is used toadjust the scan rate setting in step 284 to optimize. Preferably, thescan rate setting is adjusted in step 284 by setting it to the scan rateof whichever tracking scan performed during pre-scan that produces thebest metrics. For example, in one preferred implementation, the scanrate is optimized in step 284 by setting it to the scan rate during thetracking scan that produced the highest tracking metric.

Thereafter, whether or not tracking impacts the scan rate setting, thescan rate setting is compared against a threshold, such as in the mannerdiscussed with regard to FIG. 19, to determine in step 276 whether thescan rate is greater than the threshold. If so, the scan rate setting isadjusted in step 278 by reducing it below the threshold. If not, thescan rate setting is finalized at least in preparation for the pre-scan,if not in preparation for actual sample imaging. For example, for the“High Speed” or “fast” case, where tracking has been performed the finalscan rate setting in step 280 is the scan rate that will be used duringactual measurement instrument operation.

Alternatively, the scan rate can be determined by a lookup table or anequation as follows: Scan rate=a*exp(b*maximum erroramplitude)/[Sqrt(Scan size)] with a and b have preferred values of 11and −6×10⁻⁴, respectively.

While pre-scan was previously discussed with regard to FIGS. 12-16, itwas done so in the context where tracking analysis and relatedoptimization was either not required or not performed. In contrast, FIG.21 presents a flowchart 286 depicting a preferred implementation of apre-scan method in accordance with the present invention that includesperforming tracking analysis and related optimization. Tracking analysisis employed to determine whether tracking during the pre-scan is good orpoor. If it is poor, the values of one or more operating parameters,such as one or more gains, operating setpoint, and/or scan speed orrate, are adjusted during the pre-scan to try to improve tracking. As aresult, one or more of these parameters are optimized and tracking isimproved thereby improving image quality and consistency during actualmeasurement instrument operation.

During pre-scan, the tip of the probe is engaged with the sample andstays at one point of sample surface with zero scan size. During thistime, automatic gain tuning is also performed 290 to optimize one orboth of I-gain and P-gain. After the gain tuning, the tip starts topre-scan on the sample with the user input scan size. Finally, trackinganalysis is also performed 292 during the pre-scan to determine oroptimize at least a plurality of measurement instrument operatingparameters, including preferably scan rate or scan speed, based on suchparameter settings when the best tracking metrics are obtained.

While FIG. 13 previously discussed discloses one type of pre-scanscanning pattern that can be used where bi-direction tracking analysisisn't being performed, FIGS. 22 and 23 illustrate two examples ofpre-scan scanning patterns well suited for tracking analysis andoptimization. FIG. 22 illustrates a pre-scan scanning pattern 294 whereeach and every scan pass 186′ is a bi-directional tracking scan fromwhich information can be obtained to perform tracking analysis andoptimization. The spacing of the transversely extending jogs 188 can bevaried, such as when it is desired to increase tracking scan density,and have been set so adjacent tracking scans 186′ are spaced well enoughapart to facilitate drawing clarity. Routine testing and experimentationcan be employed to determine optimal spacing between adjacent trackinglines as the spacing can be fixed or vary depending on thecircumstances, application and other factors.

FIG. 23 illustrates a similar pre-scan scanning pattern 296 where everyother scan pass 190 is a single-direction or unidirectional scan pass190 where no tracking analysis is performed. The remainder of the scanpasses 186′, which is each scan pass 186′ disposed between a pair ofunidirectional scan passes 190, are bi-directional tracking passes.

FIG. 24 illustrates a preferred method 298 of setting and preferablyoptimizing gains during the pre-scan, steps 224-232 of which aredepicted in FIGS. 15 and 16 in less detail. In the present method 298,the amplitude error signal, E, is monitored 300 during each scan pass,186′ and/or 190 of the pre-scan. The maximum error, E_(max), obtained iskept track of in step 302 by storing it in memory, e.g., memory registeror storage location, storing it on computer readable media, or storingit in some other manner. E_(max) preferably is continually updated asneeded as the pre-scan progresses such that when the pre-scan iscompleted E_(max) represents the highest value of the amplitude errorsignal measured of all of the scan passes of the pre-scan.

Thereafter, in step 304 the maximum error, E_(max), is divided by apredetermined fixed ratio, R, and compared against the maximum amplitudenoise, N_(max), measured to determine if the E_(max),/R ratio isacceptable. While N_(max) can be the maximum noise value measured duringthat part of the automatic gain tuning method that takes place prior tothe pre-scan, in the preferred method depicted in FIG. 24, N_(max)preferably is the maximum noise value obtained during the pre-scan.

In one preferred implementation of the method 300 not shown in FIG. 24,the product, E_(max),/R, is acceptable if it falls within a certaindesired range or buffer zone of N_(max). For example, in a currentlypreferred implementation, E_(max),/R is acceptable only if it fallswithin a predetermined proximity, p, of the maximum noise value,N_(max).

If acceptable, the I-gain and P-gain are kept at their current settings306, which preferably are the same settings to which they wereprovisionally set during the automatic gain tuning that took placebefore initiation of the pre-scan. Preferably, these settings will thenbe used during actual measurement instrument operation 308. However, ifdesired, as is shown in dashed line in FIG. 24, the gains can be checkedin step 310 to determine whether I-gain exceeds I_(max) or P-gainexceeds P_(max). These maximum values can be calculated or otherwiseobtained, such as during automatic gain tuning prior to pre-scan orretrieved from a lookup table, data table, memory storage location, orthe like.

If unacceptable, I-gain and P-gain preferably are set in step 312 so thefixed ratio I÷R or (I-gain or P-gain)÷R is met. For example, if desired,I-gain can be set so the fixed ratio I-gain÷R is met and P-gain can beset so the fixed ratio P-gain÷R is met. In another preferredimplementation, the values of both gains are chosen so the fixed ratioI-gain÷R is met.

Thereafter, a check is made in step 310 whether the I-gain exceedsI_(max) and whether the P-gain exceeds P_(max). If either is exceeded,the pre-scan continues 314 such that another iteration of the gaintuning loop of method 298 is carried out during the pre-scan. Althoughnot shown in FIG. 24, whichever gain exceed its maximum preferably isreduced to a value no greater than the maximum. If desired, this can bedone to both gains, whether or not both exceeded their correspondinggain maximum. Preferably, at least the exceeding gain is backed off acertain amount or a certain percentage so as to set it to a value lessthan the maximum.

If neither gain exceeds its respective maximum value, I_(max) andP_(max), the current values for I-gain and P-gain are then set in step308 as the gain values to be used during actual measurement instrumentoperation. Preferably, in at least one preferred implementation, thegains ultimately selected for actual use are those closest in proximityto N_(max), which can also apply with regard to the respective maximumgain of each so long as the maximum gain is not exceeded.

In addition, when performing an actual image scan during measurementinstrument operation, the value for the Z-limit is automaticallyadjusted if its associated current maximum error signal,E_(max)-realtime, becomes smaller than its corresponding thresholdobtained during the pre-scan. In addition, Z-center position is alsomonitored and corrected by actuating the Z-stepper motor to the extentneeded. Finally, tip wear is continually monitored, including during thepre-scan, so that the operator can be warned as soon as practicable ofthe increased likelihood that scan image data may be compromised.

Tracking Analysis & Optimization

The method of the present invention can also include tracking analysesduring not just the pre-scan but also during actual measurementinstrument operation to determine tracking quality. In at least onepreferred implementation of a tracking quality method, tracking qualityis monitored and the value of one or more operating parameters areadjusted should tracking quality become less than desired. By constantlymonitoring and adjusting one or more operating parameters in an effortto maintain good tracking quality, measurement instrument image qualityis advantageously improved while desired tip-sample interaction ismaximized. Where the method is employed during actual sample imaging,not only is high image quality achieved but high image quality is moreconsistently obtained over the entire sample because desired tip-sampleinteraction is maximized over the entire sample.

The goal of tracking is to maintain a desired level of interactionbetween probe tip and sample by keeping the tip in contact with or asclose to the sample surface as is optimally desired, depending on modeof operation, for instance. Where the stylus or probe based instrumentis operating in contact mode, tracking seeks to keep the tip in constantcontact with the sample throughout the entire sample scanning process.Where the probe is oscillating, such as when operating in TappingMode,tracking seeks to maintain consistent tapping of the sample at thedesired level of tip-sample interaction, e.g., according to thesetpoint. However, where unwanted or unintended separation occursbetween the tip and sample, tracking suffers along with scanned imagequality.

Unfortunately, good tracking can sometimes be difficult to achieve.Sometimes tracking can adversely be affected by rough sample topography,making it difficult to maintain consistent tip-sample interaction alongthe entire sample surface. In other instances, operating parameters havebeen set to less than optimal values, making it difficult for the probeto track the sample consistently and well. For example, should scanspeed be set too high, particularly in light of the particulartopography of the sample, tracking can suffer because the tip is movingtoo fast during scanning to be able to accurately follow the sampletopography. Similar tracking problems can occur where one or both gainsare set too low or if the setpoint chosen during manual setup is weak ornon-ideal.

In an effort to address these problems, previous attempts have been madeto monitor tracking quality. One well known and commonly used qualitytracking solution is referred to as Trace-Minus-Retrace (TMR). Incarrying out TMR during a bi-directional scan, from each sample datapoint of a series of sample data points obtained at desired spaced apartlocations along the sample during the trace scan made in one direction,subtract a sample data point of a second series of spaced apart sampledata points obtained during the retrace scan made along the same scanline in the opposite direction with the retrace data point located atabout the same position on the sample as the trace sample data point.The resultant series of difference values are supposed to be indicativeof tracking quality along the entire length of the scan line that wasbi-directionally scanned. Where differences are large, TMR inferstracking quality is poor and vice versa where differences are small.Importantly, the technique is compromised if the trace locations do notalign (i.e., are offset) with the retrace locations which results in thesubtraction being imperfect, and often nonsensical. The reason for theproblem is that TMR must compare trace and retrace data at substantiallythe same location. Even small shifts in the location of features betweenthe trace and retrace can cause it to fail. This means that the TMRmethod must align the features of the trace scan and retrace scan withhigh accuracy. Non-linearity, drift and hysteresis in the scanner canmake this process-difficult if not impossible. The core problem is thatthe algorithm requires accurate knowledge of the lateral position of aspecific feature to calculate a meaningful metric.

For example, FIG. 25 illustrates part of the topography of a sample 38′that has a step 316 of relatively pronounced height or roughness. Duringthe trace pass of the bi-directional scan 328, tracking is good as thepath 318 the tip 48 of the probe travels along the surface of the sampleduring the trace pass generally matches sample surface topography.However, during the retrace pass in the opposite direction, trackingbecomes poor as the tip 48 essentially parachutes off the step 316because the tip 48 is out of contact with the sample several nanometersas shown by the dashed line path 320 in FIG. 25 before landing back onthe sample. More particularly, as the tip ceases to interact with thesample, the probe starts to oscillate as the control system operates toreturn to the setpoint by narrowing probe-sample separation to cause theprobe to again interact with the sample.

FIG. 26 is a plot 322 of the results of applying TMR to thecorresponding sets of trace and retrace data points generated from thetrace and retrace passes of the bidirectional scan depicted in FIG. 25.Where tracking is good, TMR produces virtually no difference in thecorresponding values of both sets of data points, producing the flatline regions 324 shown in the plot 322. However, where tracking is poor,namely in the region of the abutment 316 where the tip 48 parachuted offthe sample 38′ during the retrace pass, the differences betweencorresponding trace and retrace data points produce a curve 326 thatdeviates from the flat line plot regions 324 dipping negatively belowthe rest of the plot 322. Using TMR, these negative difference valuesthat produced curve 326 correctly indicate poor tracking in the areawhere the parachuting occurred.

However, as noted above, since TMR requires the location ofcorresponding trace and retrace sample data points to match, anymismatch, mislocation or misalignment that causes data points not tomatch up will induce TMR error that can wrongly indicate poor trackingquality when in fact just the opposite is the case. Unfortunately, sincemany types of piezoelectric tube scanners exhibit nonlinear behaviorduring scanning, these nonlinearities can cause the actual trace andretrace data point locations to differ leading to TMR error. In aneffort to minimize nonlinearity induced data point location mismatcherror, nonlinear piezoelectric scanners are frequently calibrated usinga multipoint calibration scheme. To further combat nonlinearity induceddata point mismatch error, software, such as of the type disclosed inU.S. Pat. No. 5,376,790, is often employed during scanning to try tocompensate for any such nonlinearity. Despite these efforts and evenwhen closed loop feedback control is employed, enough residual datapoint mismatch error occurs that TMR quality tracking determinations arenot always reliable.

For example, FIG. 27A presents a plot 330 depicting the results of abidirectional scan 332 of the surface topography of the same sample 38′shown in FIG. 25. However, in this example, scanner nonlinearity causesTMR to incorrectly indicate tracking was worse than it actually was.This is because the subset of sample data points depicting the path 334traveled along the abutment 316′ during retrace are offset or shifted inthe X-direction from where they should be relative to the sample datapoints depicting the retrace path 336 traveled in the opposite directionalong this same region 316″. As a result of scanner nonlinearity induceddata point mismatch error, TMR in this case provides a false negativeresult in FIG. 27B because its difference output plot 338 shows poortracking quality differences where none should actually exist.

At present, these problems have made TMR unsuitable for use in many, ifnot most, situations where open loop feedback control is employed,usually because of the adverse impact of scanner nonlinearities duringoperation. In some of these situations, closed loop feedback controlworks because its increased tip positional control accuracy reducesscanner nonlinearity induced data point mismatch error to an acceptablelevel. Unfortunately, there are still many instances where TMR is stillunsuitable including instances where even the residual mismatch errorstill remaining after implementing closed loop control is still toogreat as well as other instances where the sample surface is too roughor where variations in topography are too pronounced.

FIG. 28 presents a flowchart 340 illustrating a preferred method oftracking in accordance with the present invention that overcomes most,if not all, of the deficiencies that characterize TMR trackingdetermination. In the implementation of the tracking method depicted inFIG. 28, sample data point slopes 344 obtained from sets of sample datapoints generated during the trace and retrace passes of a bidirectionaltracking scan 342 are compared 346 in making a tracking determination348 whether tracking quality is good, e.g., acceptable, or poor, e.g.,unacceptable.

Importantly, in the present algorithm, mismatch errors can not bepresent because, unlike TMR, corresponding data points associated withparticular scan locations (i.e., x positions) are not compared, only rawdata independent of the actual coordinates of its corresponding scanlocation is compared. In other words, the data comparison is independentof the exact location at which the data was acquired.

Data in SPM measurements typically consists of a vertical data value (Z)for a range of XY values. The vertical data values are often topographicheights, but can also be a measurement of any interaction between theprobe and sample, as described previously. The localized slopes for thetracking algorithm may be calculated from the scan data by any suitablemethod. For example, local slopes may be computed dividing a differencein the vertical data (rise, ΔZ) between two points by the correspondingdifference in the horizontal position (run, ΔX). The slope can also becalculated by fitting a curve between a plurality of data points andthen calculating the local derivative of the fit curve. A furthersimplification can be obtained if the vertical data points are evenlyspaced in the X direction. In that case, the horizontal separation ΔXcan be considered a constant and the slope can be determined by simplymeasuring vertical inter-pixel distances (ΔZ). The slopes can becalculated using adjacent pixels, as used in the preferred embodiment,or pixels separated by any number of intervening pixels. The onlyrequirement is that the local slopes be calculated over a distance smallenough to detect the features of interest on a sample. In the preferredembodiment we calculate the slopes using the difference in Z-data valuesfrom adjacent pixels.

By using localized slopes obtained from trace and retrace sample datapoints, the method of the invention beneficially minimizes andpreferably eliminates impact from data point mismatch error. As aresult, scanner induced nonlinearities have such a negligible effectthat they do not adversely impact tracking determination. In addition, atracking determination method implemented in accordance with the presentinvention is robust in that it is insensitive to tilt error such thattilt correction need not be performed prior to or while practicing themethod in order to make a tracking determination. This also means, forexample, that sample leveling is advantageously not required before orwhile making a tracking determination.

FIG. 29 illustrates a flowchart 350 depicting another preferredimplementation of the tracking method of the invention. In thiscurrently preferred method implementation, a bidirectional scan 352 isalso carried out, such as during pre-scan or even during actualmeasurement instrument operation (e.g., when actually imaging a sample)such that a trace scan pass and retrace scan pass are performed along asingle common scan line of the sample. Thereafter, inter-pixeldifferences of data from the same scan-pass are determined 354 for thesample data obtained during both the trace scan pass and the retracescan pass. Notably, the data values of interest (sometimes referred toherein as “samples”) for making a tracking quality determinationaccording to this preferred embodiment are localized measurements of theslopes traversed by the tip.

In a preferred inter-pixel difference determination methodimplementation that preferably is capable of being carried out in step354, adjacent consecutive sample data values, i.e., pixel values, for atleast a plurality of consecutive data pairs of a scan pass (preferablythe same scan pass) are subtracted to obtain the difference betweenthem. Thus, for at least this particular case, the inter-pixeldifference corresponds to tip travel slope in the localized region ofthe path traveled by the tip between the two sample data values of theparticular scan pass from which the difference was determined. In acurrently preferred inter-pixel difference determination method carriedout in step 354, inter-pixel difference data are calculated for allconsecutive pairs of adjacent sample data values (for example, N−1samples, where N is the pixels per line, e.g., 256, 512, etc.) for boththe trace scan pass and retrace scan pass of a bi-directional trackingscan that preferably is the current bi-directional tracking scan. Theresultant inter-pixel data is kept together or otherwise groupedtogether based on the scan pass from which it originated.

To provide a better idea of at least one advantage determining suchinter-pixel difference data provides, reference is additionally made toFIG. 30 which illustrates a graph 376 showing two plots 378 and 380 ofcalculated inter-pixel difference data with one plot 378 displayingtrace inter-pixel difference data and the other plot 380 displayingretrace inter-pixel difference data. The inter-pixel difference data foreach plot 378 and 380 is arranged by scan line position or location,which in this particular example is disposed along the X-axis, e.g., inX-direction.

Though shown for consecutive pixel differences, the method of thepreferred embodiment is operable when considering non-consecutive pixeldifferences as well as alternately analyzed sample selections.

Referring once again to the preferred implementation of the trackingdetermination method depicted in FIG. 29, the inter-pixel differencedata, though already based on whether it originated from data generatedduring the trace or retrace scan pass, is further grouped into fourseparate categories 358-362. For example, in the preferred methodimplementation shown in FIG. 29, the trace scan pass difference data isdivided into two groups with one group holding all ascending slopevalues, i.e., the positive values, and the other group holding alldescending slope values, i.e., the negative values. The same re-groupingis done for the retrace scan pass difference data. For example, in thepreferred implementation of the method illustrated in FIG. 29, all ofthe trace inter-pixel difference data having a positive or ascendingslope is put in the Trace-Ascending group or bin 358, all of the traceinter-pixel difference data having a negative or descending slope is putin the Trace-Descending group or bin 360, all of the retrace inter-pixeldifference data having a positive or ascending slope is put in theRetrace-Ascending group or bin 362, and all of the retrace inter-pixeldifference data having a negative or descending slope is put in theRetrace-Descending group or bin 364.

Thereafter, each newly grouped set of inter-pixel difference data issorted 366 preferably by arranging the inter-pixel difference datavalues within each group 358-364 from highest value to lowest value,i.e. in descending order. In a currently preferred implementation, eachvalue of the data within the groups containing negative values, e.g.,groups 360 and 364, is converted to its absolute value preferably beforesorting takes place. If desired, this can also be done after sorting andcan also be done for the data in all of the groups 358-364.

Once sorted, one or more comparisons, preferably a plurality ofcomparisons 368 and 370, are made to determine one or more trackingmetrics that are or represent tracking quality determinations. Forexample, the extreme values of the slope in the Trace scan can becompared to the extreme values of the slope in the Retrace scan. In amore sophisticated implementation, the maximum value or maximum valuesof the Trace-Ascending and Retrace-Descending inter-pixel differencedata values are compared against one another such as in accordance withthe corresponding Trace-ascending and Retrace-descending plots 384 and386 shown in the graph 388 of FIG. 31. Where one or more maximuminter-pixel difference (slope) values of different plots significantlydiffer for the larger absolute slope values, as are located at the leftside of plot 388 in FIG. 31, poor tracking can be inferred. Conversely,where there is little or no difference, e.g., 10% or less difference, incorresponding maximum values, good tracking can be inferred.

When tracking is ideal, the two maximum absolute slopes agree, so theratio is 1. In the case in which descending slopes are less steep thanascending slopes, i.e., an example of poor tracking, the ratio of thisfirst metric is lowered from 1 toward 0.

This simple ratio has tremendous power compared to the prior art becauseit is self-normalizing. That is the metric scales substantially onlywith the quality of the tracking, and is substantially independent ofthe surface roughness of the sample. This is in stark contrast with theconventional TMR metric in which the amplitude of the Trace MinusRetrace signal depends on the height of the feature being scanned inaddition to the quality of the tracking. Since the tracking metric inthe current invention is related to the ratio of the local surfaceslopes, it normalizes out variations in sample topography. By taking theratio of slopes, the height of the local topography is divided out. Morespecifically, the ratio always tends towards one when the tracking isperfect, independent of the sample topography.

This self-normalizing feature allows the tracking metric to be used as afixed reference for automatically optimizing AFM operation. Theself-optimizing AFM can always target achieving a value of the trackingmetric above a certain threshold. For example, we have found that atracking metric above 0.85 (for example, based on a comparison of data(e.g., slopes) corresponding to the trace and retrace scans) generallyindicates a high quality image, over a wide range of sample types andsample roughnesses. Using this property, the inventors have developedthe algorithms described elsewhere in this specification toautomatically adjust the scan control parameters of the SPM until thetracking metric is optimized or at least above a desired thresholdvalue.

Note that it is also possible to select a range of slope measurements toimprove the performance of the algorithm, especially in the presence ofnoise. A noise spike can give a spuriously large value of absolute slopethat exceed the true sample slope. For this reason it may be desirableto add a noise rejection filter on the slope data set or use a subset ofthe slope data to avoid the extreme values that may result from noisespikes. One possibility, for example, is to exclude the top 5% of slopevalues as a means of rejecting noise spikes. In some cases, using alarger range of local slope values provides data averaging that alsosuppresses the effect of noise spikes. For example, using a range of75%-100% of the maximum slope includes the extreme value and aneighboring range.

It is also possible in some circumstances to use a noise rejectionfilter that rejects slopes that are more than some number K times thestandard deviation of the slope distribution. A reasonable value for Kis 2-3.

Notably, this metric qualifies tracking with respect to the largestslopes occurring in an assessment data set, regardless of the absoluteslope magnitudes present. Notably, even when scanning is nonlinear(i.e., evenly timed data acquisition does not yield evenly spaced samplesites), the variation in Δx is proportional to the variation in scanvelocity, which typically is a small fraction of average scan velocity.

If desired, a double check can be provided to confirm. For example, withadditional reference to the graph 390 of FIG. 32, the maximum values ofthe Trace-descending and Retrace-ascending groups 392 and 394 can becompared in the same manner. Tracking is good if they are substantiallythe same or fall within a certain acceptable limit or tolerance of oneanother and tracking is poor where the differences between correspondingmaximum values are too great.

The graph 396 of FIG. 33 also illustrates this, perhaps a bit moresimply and clearly than, for example, FIG. 32 does. Where the ascendingmaximum value, a_(max), is larger than the descending maximum value,−d_(max), by too great an amount, tolerance or percentage, tracking isdetermined to be poor or unacceptable 372 (FIG. 29). Conversely, wherea_(max) and −d_(max) are the same or substantially the same such thatthey are within a desired amount, tolerance or percentage, including ofone another, then tracking is determined to be good or acceptable 374(FIG. 29).

In one preferred embodiment, an average can be taken of both of thesetracking metrics to obtain a relative tracking metric particularlyuseful, for example, in determining tracking quality where the samplesurface is relatively smooth or flat. In another preferred embodiment,where the tip apex approach slopes differ along the fast scan axis, thesteeper slope, producing the lower metric value, is the more accuratetracking indicator and is relied on preferentially. Other embodimentsaverage the higher slope values and/or exclude some of them forsignal-to-noise improvement. Another slope sample based tracking metricis absolute in that it provides the maximum descending slope observed ineither of the first and second assessment dataset. This is provided asan angle related to the instrument Z-axis. Specifically, the arctangentis taken of the largest falling difference, −Δz_(min) divided by theaverage interpixel travel distance, Δx=(scan range)/n. With this metric,the length of the line scanned and the number of samples taken enter thecalculation.

FIG. 34 illustrates a flowchart 400 of another preferred implementationof a tracking quality method of the present invention where trackingquality is employed as a control variable that is used to adjust andpreferably optimize a value of at least one operating parameter, such asscan speed or scan rate, operating setpoint, and/or one or both gains.The optimal value of the parameter or parameters being optimized is setat the value when tracking quality is highest or best. In anotherpreferred method implementation, one or more tracking scans can andpreferably are repeated using different parameter values until trackingis suitable. Thereafter, the parameter is either set to that value or tothe value at which it was set during the particular bi-directionaltracking scan that produced the best tracking or highest trackingquality. Where an actual imaging scan is being performed, the parametervalue is simply updated to correspond to the value that produced thelast best tracking quality.

In the method depicted in FIG. 34, slopes are converted into absolutevalues in step 402 and a check is made in step 404 whether the trackingquality output in step 372 or 374 is suitable. If tracking quality isnot suitable, then the value of the particular operating parameter beingoptimized is adjusted, such as by incrementing it, etc., before thebi-directional tracking scan is performed using the adjusted operatingparameter value(s). Preferably, the scan is performed again at the samescan line, but can be performed at a different scan line location, ifdesired. If tracking quality is suitable, a check is made in step 408 todetermine whether the pre-scan or actual image scan is complete. If not,the bi-directional scan line setting is incremented to the next scanline and the whole process preferably is repeated.

In addition to the aforementioned, the n-th steepest ascending slope andthe n-th steepest descending slope can be compared with the comparisonmade based on the absolute value of at least the negative slope. Inanother preferred tracking metrics implementation, the n-steepestascending slopes can be averaged and compared against a correspondingaverage of n-steepest descending slopes.

In another preferred implementation, curve fitting can be employed, suchas where it is desired to compare curves fitted to some or all of theascending slope data against corresponding descending slope data. In onepreferred implementation, a polynomial fit is made to the n-largestascending slope samples plotted in descending order by size. Apolynomial fit is likewise made to the n-largest descending slopesamples also plotted in descending order by size. Thereafter, each fitas applied to the maximum slope sample is used as its substitute intracking metric determinations. In some instances, it may be desired tofilter at least some of the slope data. For example, if desired, one ormore of the steepest ascending and descending slope values can be thrownout or otherwise excluded before determining any one of the trackingmetrics discussed above.

Although the best mode contemplated by the inventor for carrying out thepresent invention is disclosed above, practice of the present inventionis not limited thereto. It will be manifest that various additions,modifications and rearrangements of the features of the presentinvention may be made without deviating from the spirit and scope of theunderlying inventive concept. The scope of still other changes to thedescribed embodiments that fall within the present invention but thatare not specifically discussed above will become apparent from theappended claims.

1. A method of performing setup of a probe-based measurement instrumenthaving a probe and a position-affecting controller comprising: (a)automatically determining at least a plurality of setup operatingparameters of the probe-based measurement instrument; (b) scanning theprobe over a sample using the at least plurality of setup operatingparameters determined in step (a); and (c) obtaining sample-related datatherefrom; and wherein none of the setup operating parameters areempirically determined prior to initiating the scanning step.
 2. Amethod of performing setup of a probe-based measurement instrumenthaving a probe and a position-affecting controller comprising: (a)manually initiating automatic determination of at least a plurality ofsetup operating parameters of the probe-based measurement instrument;(b) scanning the probe over a sample using the at least plurality ofsetup operating parameters determined in step (a); (c) obtainingsample-related data therefrom, and wherein the automatic setup operatingparameter determination step (a) comprises (1) performing automaticparameter tuning, (2) determining a plurality of probe-samplepre-engagement settings, (3) performing automatic gain adjustment, (4)performing a pre-scan of the sample, and thereafter (5) optimizing atleast a plurality of pairs of operating parameters.
 3. The method ofclaim 2, wherein the automatic parameter tuning step (1) comprises (i)oscillating a cantilever of the probe, and (ii) determining a resonantor natural frequency of the cantilever.
 4. The method of claim 3,wherein scan size is set to zero during the automatic parameter tuningstep (1).
 5. The method of claim 2, wherein the probe-samplepre-engagement settings determination step (2) comprises (i) checkingeach operating parameter against a corresponding safe operatingparameter setting or setting range, and (ii) adjusting each operatingparameter outside the safe operating parameter setting or setting rangeso it the same as the safe operating parameter setting or lies withinthe safe operating parameter setting range.
 6. The method of claim 5,wherein the safe operating parameter setting or setting range for atleast a plurality of operating parameters is stored in a lookup table.7. The method of claim 5, wherein before step (i) the step of checkingwhether the probe-based measurement instrument has a safe mode andputting the probe-based measurement instrument into safe mode if theprobe-based measurement instrument has safe mode capability.
 8. Themethod of claim 5, wherein steps (i) and (ii) are performed for at leastten operating parameters.
 9. The method of claim 8, wherein steps (i)and (ii) are performed for determining a safe operating parametersetting for at least integral gain, proportional gain, amplitude noise,scan size, scan rate, number of scan lines, offset voltage, and Z-limit.10. The method of claim 9, wherein steps (i) and (ii) are also performedfor determining a safe operating parameter setting for at least back offpercentage, bi-directional pre-scan I-gain, and bi-directional pre-scanP-gain.
 11. The method of claim 2, wherein the automatic gain adjustmentstep (1) comprises (i) ramping up an integral gain and a proportionalgain, (ii) monitoring amplitude noise, (iii) stopping gain ramping whena noise threshold is reached, and thereafter (iv) setting an integralgain operating parameter and (v) setting a proportional gain operatingparameter.
 12. The method of claim 11, wherein the integral gainoperating parameter set in step (iv) and is based on the integral gainwhen gain ramping is stopped in step (iii) and the proportional gainoperating parameter set in step (v) is based on the proportional gainwhen gain ramping is stopped in step (iii).
 13. The method of claim 12,wherein gain ramping is stopped in step (iii) when the onset of feedbackloop oscillation is detected.